The most recent indications for the use of tibia intramedullary nails are simple horizontal or oblique fractures of the tibia, multistage breaks of the tibia shaft, and fragmented breaks of the tibia shaft. Because use of tibia intramedullary nails is now indicated for more fractures of the lower leg, a need to change the shape and nature of the nail has arisen.
Formerly, the basic purpose of an intramedullary nail was to immobilize the bone internally, with the axial force as well as torsional moments being borne by the bone itself. The only function of the nail was to maintain the longitudinal axis of the bone upright. This meant that relatively thin, flexible nails could be used, which have the advantage that they can be adjusted to the medullary cavity. This adjustment is particularly important in the insertion of the nail, since the entry point of the nail is not in line with the longitudinal axis of the bone. The entry point is located on the tuberositas tibia, slightly proximal to the patellar tendon attachment. After the medullary cavity has been opened with an awl and the medullary cavity has been drilled, the nail is driven in. The problem with driving in the nail is that after crossing the medullary cavity, the nail reaches the posterior cortex, and can be driven in further only if its shape is deformed. With soft bones and young patients, the tip of the nail sometimes punctures the posterior cortex.
To prevent a perforation of the posterior cortex, the method known as bunch-nailing (for example, according to German Auslegeschrift AS 23 41 439) has been proposed. In this method, wires approximately 2.0 mm thick are pushed into the medullary cavity. The advantage of this method is that the individual wires are very flexible and can adjust well to the shape of the medullary cavity. In this known method, the medullary cavity is filled up with individual wires, whereupon it becomes possible to splint the bone.
Bunch-nailing has become generally accepted in treating short oblique fractures in the mid-shaft range of the tibia. The disadvantages of this method become evident, however, when a fragmented or multistage fracture must be treated. The individual wires are not sufficient to protect a fracture in the axial direction or against rotation. To preserve the length of the bone and to protect against rotational movements, only a stiff and rigid implant is suitable, preferably one which may be locked by screws inserted proximally and distally to the fracture area.
The tibia intramedullary nails known in the prior art, which create an axial stability and a rotational stability of the fracture, have a short proximal end segment, or crown hook, and a distal segment having a straight part with a rounded tip, which simplifies stringing together of the fragments. However, as described above, these nails are rather severely deformed when inserted, so that the nail can bend plastically in the longitudinal direction. If four-fifths of the tibia nail is driven in, the crown hook penetrates the tuberositas tibia, and thereby relieves the bending demand made upon the stud. This relief can be such that when the stud is fully driven in, it lies loosely in the medullary cavity.